Q-compensated viscoelastic reverse time migration in crosswell seismic imaging

Abstract

Abstract Viscoelastic reverse time migration (RTM) is a practical approach to compensats for attenuation effects in migration, commonly studied in surface seismic research. Compared with conventional surface seismic imaging, the sources and receivers of crosswell seismic imaging are distributed in different wells with higher main frequencies and lower surface noises. The finer structures can be imaged. In this paper, we apply attenuation compensated RTM in crosswell migration to improve the resolution of images in attenuation regions. We solve the viscoelastic equations using the constant Q model because of its advantage of decoupling the amplitude and phase. The fractional-order amplitude and phase Laplacian operators are used. By spectral ration techniques, we observe the relationship between attenuation and frequency in crosswell seismic imaging. We describe the alignment and muting of direct P- and S-waves from full waves in detail. Synthetic examples demonstrate that Q-RTM images the geological structure more clearly than the traditional RTM. We reveal that compensated images describe the three-layer model, tilted fractures and randomly distributed caves more accurately. As the tilted angles increase, only two end points of the tilted fracture can be identified by conventional RTM, the boundary is blurred. We find that caves far from the source well can barely be imaged. By comparison, the compensated RTM approach obtains precise migration results of tilted fractures with arbitrary dip angles and caves. Finally, to approximate the real measurement data, noise is added to the viscoelastic data of the five-layer model. The effective noise immunity in crosswell seismic applications is verified.